The invention relates to pneumatic tires which have improved snow traction and tread wear, and improved noise and wet and dry handling characteristics.
It is a continuing goal in the art to improve the properties of pneumatic tires. This continuous improvement is driven by competition between the tire manufacturers and also, to some extent, by a drive for improvement by vehicle manufacturers. To some extent, improvements in original equipment (OE) tires are driven by competition between the automobile manufacturers.
Sometimes, improvements manifest themselves in entirely new and revolutionary tire constructions, and sometimes the improvements comprise incremental changes that are required of a tire manufacturer by a vehicle manufacturer to meet OE specifications. Relatively small changes in tread design, and changes in and use of materials, can cause significant differences in tire properties, and such differences may mean the difference between meeting specifications and being rejected by the OE customer.
Tires similar to the tire of the invention have been used in OE accounts in previous years with satisfactory performance. As changes in vehicle design, and especially the design of the suspension of a vehicle takes place, changes in the tires are required, always with the goal of improving the performance of the tire/vehicle combination.
It is an object of the present invention to improve the performance of a tire line that is currently in commercial use.
Other objects of the invention will be apparent from the following description and claims.
Definitions
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cContact Patchxe2x80x9d refers to a section of footprint, in a footprint that is divided into sections by wide void areas, that maintains contact with the ground.
xe2x80x9cCrownxe2x80x9d refers to the circumferentially outermost portion of the carcass substantially within the width limits of the tread.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under design load and pressure.
xe2x80x9cFootprint Net-to-grossxe2x80x9d refers to the actual footprint of a deflected tire and is the ratio of the ground contacting surface area of the tread to the total tread footprint area including the groove void area.
xe2x80x9cGroovexe2x80x9d means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight, curved, or zig-zag manner. Grooves ordinarily remain open in the tire footprint. Circumferentially and laterally extending grooves sometimes have common portions and may be sub-classified as xe2x80x9cwidexe2x80x9d or xe2x80x9cnarrowxe2x80x9d. Grooves may be of varying depths in a tire. If such narrow or wide grooves are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming xe2x80x9ctie barsxe2x80x9d tending to maintain a rib-like character in the tread region involved.
xe2x80x9cLugsxe2x80x9d refer to discontinuous radial rows of tread rubber-in direct contact with the road surface.
xe2x80x9cNet-to-grossxe2x80x9d refers to the ratio of the ground-contacting surface of a tread to the total tread area.
xe2x80x9cPneumatic tirexe2x80x9d means a laminated mechanical device of generally toroidal shape (usually an open-torus) having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on the wheel of a motor vehicle, the tire through its tread provides traction and contains the fluid that sustains the vehicle load.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d are used to mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cShoulderxe2x80x9d refers to the upper portion of sidewall just below the tread edge.
xe2x80x9cSidewallxe2x80x9d means that component which comprises a portion of the outside surface of a tire between the tread and the bead.
xe2x80x9cSipesxe2x80x9d refer to small slots molded into ribs of a tire that subdivide the tread surface and improves traction characteristics. Sipes tend to close completely in a tire footprint.
xe2x80x9cSlotsxe2x80x9d are elongated void areas formed by steel blades inserted into a cast or machined mold or tread ring. Slots ordinarily remain open in a tire footprint. In the appended drawings, slots are illustrated by single lines because they are so narrow.
xe2x80x9cTreadxe2x80x9d means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
xe2x80x9cTread widthxe2x80x9d means the arc length of the road contacting tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.
xe2x80x9cTurn-up plyxe2x80x9d refers to an end of a carcass ply that wraps around one bead only.
A pneumatic tire comprises at least a pair of annular beads, at least one carcass ply wrapped around the beads, tread disposed over the carcass ply in a crown area of the tire, and sidewalls disposed between the tread and the beads, the tread pattern having lugs formed by the intersection of lateral grooves and circumferential grooves, the improvement comprising a tread pattern having 80 to 105 pitches and a sipe density in the lugs of 1.0 to 1.1 sipes per pitch.
In the illustrated embodiment, the tire has 4 circumferential grooves, and 98 pitches in a PJ-5 pitch sequence. The tire has a combined net-to-gross ratio in the center and intermediate lug portions of 0.58 to 0.62, and a net-to-gross ratio in the shoulder portions of 0.75 to 0.8 and an overall net-to-gross ratio of 0.646.
The illustrated tire has a rounded footprint shape and a footprint factor of 1.2 to 1.5, preferably 1.2 to 1.4.
The sipes in the shoulder region of the tire are at substantially 90xc2x0 with respect to the equatorial plane of the tire. Also, the lateral grooves are at substantially fill tread depth in the shoulder region of the tire and are graded to less than full tread depth at the center of the tire. Specifically, the lateral grooves are at substantially full tread depth in the shoulder region of the tire with tie bars xc2xd tread depth, and are graded to about ⅔ tread depth at the center of the tire.